Psychiatrists said that Riggi suffered from narcissistic, paranoid and histrionic disorders.

The child-killer was imprisoned at Cornton Vale prison in Stirling, Scotland, before being transferred to Rampton Secure Hospital in Nottinghamshire, where some of Britain's most disturbed criminals are held.

The move came two years after she was allegedly disfigured for life with a razor-blade by a fellow inmate at the all-female Scottish prison in 2011.

Riggi had to be transferred to Rampton Secure Hospital – where Soham murderer Ian Huntley was also treated – after Scottish Prison Services deemed there to be no other place to secure her safety.

VICTIMS: The smiling faces of the three chldren killed by their mother [PA]

It is thought that Riggi died of natural causes as she had an on-going eating disorder as well as suffering the effects of the leap from the balcony in 2010.

A Nottinghamshire Police spokeswoman said: "We can confirm that we were called to Rampton in the early hours of this morning to the death of a woman. It's not being treated as suspicious and we are preparing a file for the coroner."

A Senior Scottish Prison Services insider added: "Quite apart from her very severe and deadly mental health issues, Riggi also suffered some serious injuries taking a header from three floors up.

"She had issues with food for a long time before she killed her children and anorexia or bulimia was always a concern."

During Riggi's sentencing at the High Court in Glasgow, Lord Bracadale said that while Riggi's responsibility was diminished she was still accountable for her actions.